This project focuses on the genetics of traits related to asthma, including asthma, atopy, total IgE, and specific IgE, and comprises a number of small studies in different populations. The first project is a segregation analysis of total serum IgE levels (tIgE) in an isolated fishing village in the Chesapeake Bay; Tangier Island, VA. Under complete ascertainment, phenotype data were available on 70% of the population with all individuals connected in a single complex pedigree dating back to 1722. Analyses included: 1) the segregation analysis of tIgE, for which use of only restricted genealogical data is feasible; and 2) the impact of utilizing this restricted genealogical information in a segregation analysis of a quantitative trait. The second project focused on total and specific IgE to dust mites indigenous to the Barbados. The main objective of this study was to determine prevalence and correlates of sensitivity (Blo t, Der p 1) to these mites in families with asthma. The sample included 481 members of 29 families from Barbados ascertained through two asthmatic sibs. Blo t 5 sensitivity was present in 46% of subjects and was associated with younger age, higher total serum IgE level, and a three-fold increased prevalence of asthma. Der p 1 sensitivity was less common (27%) and showed similar associations with age, IgE, and asthma. Blo t 5 is the predominant sensitizing mite allergen in these Barbadian families with correlates similar to Der p 1. Concomitant sensitization to Der p 1 appears to identify a more reactive subgroup of individuals at a higher risk of asthma.